An 8 mm-high NiCoCrAlYTa coating was epitaxially built-up on a directionally solidified (DS) Ni-based superalloy blade tip by electro-spark deposition.Epitaxial morphologies of the coating and its microstructural characteristics were investigated by means of SEM,XRD and TEM etc.It is observed that the fine column-like dendrites originated from the γ'-particles or γ'-clusters of the DS substrate and are un-continuously coarsened.The β-phase particles precipitate and grow eutectically with the γ-phase.The orientation of fine column dendrites depends on electro-spark deposition processing parameters and the microstructure can be characterized with superfine γ and β phases.
Three kinds of MCrAlY coatings with different aluminum contents （5%, 8%, 12%） were prepared by electrospark deposition （ESD）, their microstructure and oxidation behavior were studied by SEM and XRD. The results showed that the phase composition of the coatings changed from single γ-Ni to γ-Ni＋β-NiAl hypoeutectic to γ-Ni＋β-NiAl hypereutectic with increasing aluminum content, and their solidification morphologies changed from cluster of cellular structure to cellular dendrites to coarse dendrites with secondary arms. When exposed at 1000 ℃, the coatings with higher Al content had a stronger tendency to form θ-Al2O3 in the initial several hours. After 100 h of oxidation, a dense and adherent α-Al2O3 scale formed on all of the three coatings but the thickness of α-Al2O3 scale and the amount of remaining θ-Al2O3 increased with increasing Al content. These results revealed different characteristics of ESD MCrAlY coatings which could provide scientific guidance for industrial application.
MCrAlY/TaC metal matrix composite coatings with 10, 20 and 30 wt.% TaC have been successfully produced by electrospark deposition （ESD）. The effects of TaC content on microstructure, hardness and oxidation behavior of the composite coatings were studied. The results showed that the composite coatings were composed of superfine 9＇ columnar dendrite and large TaC particles dispersedly distributed. The hardness was enhanced but oxidation resistance of the composite coatings was reduced with increasing TaC contents.
